The present invention relates to a toner and an image forming apparatus which help for achieving a fusing unit having a simple structure and can prevent the occurrence of filming on a developing unit.
FIG. 1 is an illustration for explaining a conventional image forming apparatus with an intermediate transfer member. A rotary developing unit 1 comprises developing rollers of four colors: Y, M, C, K. The developing unit 1 turns to bring every one of the developing rollers in contact with the photoreceptor 2 for every rotation of a photoreceptor 2, just like a revolver. After the photoreceptor 2 is uniformly charged by a charging unit 3, images for the respective colors are exposed to light so as to form electrostatic latent images on the photoreceptor 2. The photoreceptor 2 comes in contact with the developing rollers Y, M, C, K to develop respective color images. Because of contact between the photoreceptor 2 and an intermediate transfer member 5, these color images are transferred to the intermediate transfer member 5 (primary transfer). Residual toner particles remaining on the photoreceptor after the transfer are removed by a cleaning unit 4. As the four color images are superposed on each other on the intermediate transfer member 5, a paper 8 is conveyed and a secondary transfer roller 7 is brought in contact with the paper 8. At this point, secondary transfer bias voltage is applied by a power source, not shown, so as to transfer the superposed color images to the paper 8 at once (secondary transfer). The secondary transfer roller 7 can swing to come in contact with the intermediate transfer member 5 in the direction of the double arrow. While color images are primary transferred and toned on the intermediate transfer member 5, the secondary transfer roller 7 is spaced apart from the intermediate transfer member 5. During the secondary transfer, the secondary transfer roller 7 is in contact with the intermediate transfer member 5 via the paper. Residual toner particles remaining on the intermediate transfer member 5 after the secondary transfer are removed by a cleaning unit 6.
In the image forming apparatus having the aforementioned structure, as shown in FIG. 2, the paper 8 with a transferred multi-color image is passed through a fusing unit composed of a heat roller 10 and a buck-up roller 11, thereby fusing the toner on the paper. However, the fusing unit of this type has disadvantages that a paper may be caught by the heat roller and that melt toner is caused, resulting in xe2x80x9chot offsetxe2x80x9d. To prevent these problems, as shown in FIG. 3, an oil application roller 12 is provided to apply oil to the heat roller 10.
Conventionally, the problems of the fusing unit such as catching a paper and xe2x80x9chot offsetxe2x80x9d have been solved by applying oil to the heat roller to improve the release characteristics between the toner and the heat roller. This method, however, requires the control for applying oil, resulting in a complex structure and an expensive and large fusing unit, and requires the replacement of the oil application roller, losing user""s convenience. To solve these problems, another method without using the oil application roller, so-called xe2x80x9coil-less fusing methodxe2x80x9d has been proposed. This method is improving the release characteristics by using fluorocarbon material as the outer layer of the heat roller and increasing the amount of wax to the toner.
Now, description will be made as regard to the developing unit. As shown in FIG. 4, a supply roller 21 rotates in a direction opposite to the rotational direction of a developing roller 20 and is arranged to be in contact with the developing roller 20 so as to rub the toner onto the surface of the developing roller 20 to cause frictional electrification. A regulating blade 22 regulates the toner on the surface of the developing roller 20 into a predetermined thickness and uniformly charging the toner. After that, the toner on the developing roller 20 is supplied to the photoreceptor 2. When the amount of wax contained in the toner is large, some toner particles adhere to the regulating blade 22, thus leading to the occurrence of filming. For example, when an image of light duty is developed, toner particles are selected to be used so that toner particles of large particle size and small particle size are left in the developing unit. These left toner particles are also used when suitable toner particles are consumed. As the concentration of toner particles of small particle size is accordingly increased, such particles remain in concavities of the surface of the developing roller for a long time, thus leading to the occurrence of filming on the regulating blade. In case of using a toner including a large amount of wax for achieving xe2x80x9coil-less fusing methodxe2x80x9d, when heat and pressure are applied to the toner within the developing unit, the wax adheres to the regulating blade. This may cause filming at relatively earlier stage and may shorten the life of the developing unit as compared to the conventional one.
It is an object of the present invention to solve the aforementioned problems and to achieve both the xe2x80x9coil-less fusingxe2x80x9d and the elongation of lifetime of a developing unit.
Therefore, the first aspect of the present invention is a toner being characterized in that the external additive coating ratio of toner particles of which mother particles have equivalent particle diameters larger than the mean particle diameter of the toner is set to be lower than a virtual reference curve in synchronous distribution of the equivalent particle diameters of synchronous external additive particles relative to the equivalent particle diameters of mother particles, wherein assuming that the external additive coating ratio of a toner particle of which a mother particle has an equivalent particle diameter equal to the mean particle diameter of the toner is a reference value, the virtual reference curve is obtained to satisfy that the external additive coating ratio is constant at the reference value.
The first aspect of the present invention is also characterized in that the external additive coating ratio at the reference value is in a range from 80% to 120%.
The first aspect of the present invention is further characterized in that the mean particle diameter of synchronous toner particles with external additive particles adhering thereto is set to be smaller than the means particle diameter of the entire toner, whereby the external additive coating ratio of toner particles with diameters larger than the mean particle diameter of the toner is set to be lower.
The first aspect of the present invention is furthermore characterized in that the liberated particle ratio of mother particles with diameters smaller than the mean particle diameter of the toner is set to be lower than the liberated particle ratio of mother particles with diameters larger than the means particle diameter of the toner, whereby the external additive coating ratio of toner particles with diameters larger than the mean particle diameter of the toner is set to be lower.
The second aspect of the present invention is a toner being characterized in that the external additive coating ratio of toner particles of which mother particles have equivalent particle diameters smaller than the roughness of a developing roller is set to be higher than a virtual reference curve in synchronous distribution of the equivalent particle diameters of synchronous external additive particles relative to the equivalent particle diameters of mother particles, wherein assuming that the external additive coating ratio of a toner particle of which a mother particle has an equivalent particle diameter equal to the roughness of the developing unit is a reference value, the virtual reference curve is obtained to satisfy that the external additive coating ratio is constant at the reference value is a reference.
The second aspect of the present invention is further characterized in that the external additive coating ratio at the reference value is in a range from 80% to 120%.
The second aspect of the present invention is furthermore characterized in that the mean particle diameter of synchronous toner particles with external additive particles adhering thereto is set to be smaller than the means particle diameter of the entire toner, whereby the external additive coating ratio of toner particles with diameters smaller than the roughness of the developing roller is set to be higher.
The second aspect of the present invention is still further characterized in that the liberated particle ratio of mother particles with diameters smaller than the roughness of the developing roller is set to be lower than the liberated particle ratio of mother particles with diameters larger than the roughness of the developing roller, whereby the external additive coating ratio of toner particles with diameters smaller than the roughness of the developing roller is set to be higher.
The third aspect of the present invention is a toner being characterized in that the external additive coating ratio of toner particles of which mother particles have equivalent particle diameters larger than the roughness of a developing roller is set to be higher than a virtual reference curve in synchronous distribution of the equivalent particle diameters of synchronous external additive particles relative to the equivalent particle diameters of mother particles, wherein assuming that the external additive coating ratio of a toner particle of which a mother particle has an equivalent particle diameter equal to the roughness of the developing unit is a reference value, the virtual reference curve is obtained to satisfy that the external additive coating ratio is constant at the reference value is a reference.
The third aspect of the present invention is further characterized in that the external additive coating ratio at the reference value is in a range from 80% to 120%.
The third aspect of the present invention is furthermore characterized in that the mean particle diameter of synchronous toner particles with external additive particles adhering thereto is set to be larger than the means particle diameter of the entire toner, whereby the external additive coating ratio of toner particles with diameters larger than the roughness of the developing roller is set to be higher.
The third aspect of the present invention is still further characterized in that the liberated particle ratio of mother particles with diameters smaller than the roughness of the developing roller is set to be higher than the liberated particle ratio of mother particles with diameters larger than the roughness of the developing roller, whereby the external additive coating ratio of toner particles with diameters larger than the roughness of the developing roller is set to be higher.
The fourth aspect of the present invention is a toner being characterized in that the external additive coating ratio of toner particles of which mother particles have equivalent particle diameters smaller than the mean particle diameter of the toner is set to be lower than a virtual reference curve in synchronous distribution of the equivalent particle diameters of synchronous external additive particles relative to the equivalent particle diameters of mother particles, wherein assuming that the external additive coating ratio of a toner particle of which a mother particle has an equivalent particle diameter equal to the mean particle diameter of the toner is a reference value, the virtual reference curve is obtained to satisfy that the external additive coating ratio is constant at the reference value is a reference.
The fourth aspect of the present invention is further characterized in that the external additive coating ratio at the reference value is in a range from 80% to 120%.
The fourth aspect of the present invention is furthermore characterized in that the mean particle diameter of synchronous toner particles with external additive particles adhering thereto is set to be larger than the means particle diameter of the entire toner, whereby the external additive coating ratio of toner particles with diameters smaller than the mean particle diameter of the toner is set to be lower.
The fourth aspect of the present invention is still further characterized in that the liberated particle ratio of mother particles with diameters smaller than the mean particle diameter of the toner is set to be higher than the liberated particle ratio of mother particles with diameters larger than the means particle diameter of the toner, whereby the external additive coating ratio of toner particles with diameters smaller than the mean particle diameter of the toner is set to be lower.
The fifth aspect of the present invention is an image forming apparatus comprising at least a latent image carrier on which an electrostatic latent image is formed, a developing unit for developing the electrostatic latent image on the latent image carrier with a toner, a transfer means for transferring the developed image on the latent image carrier, and a fusing means for fusing the transferred image, the image forming apparatus being characterized in that said toner is a toner of any one of the aforementioned aspects.